Method for forecasting physical characteristics of thick steel plate



J. H. SCOTT 3,453,863

.METHOD FOR FORECASTING PHYSICAL CHARACTERISTICS OF THICK STEEL PLATE Filed March 9. 1966 July 8 1969 RECORDER. r/6

PROGRAMMER 122 ,/5 1 4 CONTROLLER r20 I73 26 P OWER SUPPLY IN VENTOR JOHN H. SCOTT W WZ4 A 7' TORNEYS United States Patent vania Filed Mar. 9, 1966, Ser. No. 532,992 Int. Cl. G011: 25/16 U.S. Cl. 73-15 2 Claims ABSTRACT OF THE DISCLOSURE A method of forecasting physical properties of a thick steel plate following heat treatment by recording the heating and cooling rates which occur during such heat treatment at a standard location in a plate having similar chemistry and thickness, and obtaining from the plate to be tested a comparatively small specimen from a similar location, placing such specimen in a furnace where it is heated and cooled at the same rate as recorded with the similar plate, and testing the specimen to determine its physical properties.

Background and summary of the invention This invention relates to a method and apparatus for simplifying the testing of thick steel plates. More particularly, this invention relates to a method and apparatus for simulating the heating and cooling cycles of thick steel plates using relatively small steel specimens and thereby reducing waste.

Steel plates used to fabricate structures such as vessels and other large equipment are frequently heat treated after fabrication of the structures. Current practices of forecasting the strength and other properties of thick steel plates (4 or more thick) to be heat treated involve the rolling of plate with excess steel. Specimens from the excess steel are cut from the plates and these specimens are heat treated in accordance with the fabricators specifications and then the specimens are tested. If these tests were not conducted, considerable cost and efforts incident to fabrication of the plates into the structure involved might otherwise be lost. This is a gamble that few fabricators can afford.

The length and width of a specimen block cast is usually two or three times (2T or 3T) the thickness of the plates. For a plate 6" thick, a block in a 3T test would necessarily have dimensions of 18" x 18 x 6". Thus for 3T testing top and bottom of a plate, 36" by the full width of the pattern is needed to be added to the rolled plate. This is a substantial portion of the plate. For a plate 96" wide of 6" gauge, over 4000 pounds is needed for testing purposes.

The reason for using such large blocks is that it is necessary to obtain test specimens with suflicient mass to duplicate the cooling and heating cycles.

Although the large specimen blocks are invariably taken from plates prior to heat treatment, at times the heat treatment is accomplished in the steel company, in which event, it may be necessary to treat and test several large specimen blocks for the purpose of determining the most favorable heat treatment for the desired end product.

It is an object of the present invention to accurately simulate the heating and cooling cycles of thick steel plates using relatively small test samples and thereby reduce waste.

The above and other objects will be apparent from the drawings and following description:

Brief description of the drawings FIG. 1 is a diagram of the control system.

Description of the preferred embodiment According to the present invention the test specimen 2 is taken from the approximate center of a block of the plate preferably at A or /3 of the plates thickness and need only be about 0.5" in thickness 01' diameter. The heating and cooling rates for steel plates of a certain chemistry must have been previously obtained by placing thermocouples in a 21 or 3T block of a plate similar in chemistry and thickness along the centerline or the quarterline or in the same location as that from which the specimen is taken. The specimen 2 has a monitoring thermocouple 4 and a control thermocouple 6 spot welded along the side thereof and the specimen is suspended in a furnace 8 by wire 10. The furnace 8 is water cooled with inlet 12 and outlet 14 in the furnace casing. In one test the furnace was a dual dielliptical aluminum reflector, water cooled unit housing two quartz tubes. The furnace, Model E2-10-2, 220 v. AC, 60-cycle, is made by Research, Inc., Minneapolis, Minn., and will heat specimens up to 1800 F. or more.

A wire 16 from the monitoring thermocouple 4 leads to recorder 18 so that an accurate history of the timetemperature treatment of the specimens during cooling and heating is recorded. A suitable recorder used in the below example is the Brown Electronic Recorder manufactured by Honeywell. This instrument is capable of recording temperatures 200-2000 F. and has a 24 Pt. recorder-type K, 120 v. AC, '60 cycle dual chart speed.

The control thermocouple 6 is connected by a wire conductor 20 to a controller 22 which in turn is connected through circuit 21 to a source of power. The controller 22 used and found suitable is the Thermac Temperature/ Power Controller operating at l)-2000 F. from a Chromel/Alumel thermocouple made by Research Incorporated. The controller uses -230 v. AC, 60-cycle at 40 amp. The controller is connected by conductor 24 to programmer 26. Programmer 26 is a conventional instrument such as that used in the below example, namely, a Research Incorporated Trak Programmer, 8. 115 v. AC, 60-cycle unit. Power supply 23 is connected to the heating units of furnace 8 through circuit 19. The controller 22 is responsive to thermocouple 6 and to programmer 26 to regulate the heating units in the' furnace. 4

Example 1 Using the above instruments arranged as shown in FIG. 1 a specimen of a steel plate of 6% gauge was taken from the plate. The steel had the following ladle chemistry:

HEAT TREATMENT 1,700 F., 6% hours, Air cool 1,350 F., 3%; hours, Furnace cool to 600 F. 1,050 F., 40 hours, Furnace cool to 600 F.

Example III A 6 /5" thick plate of A 387 Grade D plate having Yield Tensile Percent Percent strength, strength, elong. reduc. Test location 0.2%, k.s.i. k.s.i. in 2 of area Program Gool Top-RT. 770 F 64. 5 84. 7 32 73.0 49.3 71.8 70.8

2T X 2T Top-RT. 770 F 61.4 87. 3 31 73. 1 54.3 75.5 21 66.7

Program C0ol-- Bottom-RT. 770 F-. 51. 7 78. 3 31 75. 3 38. 4 66.1 26 67.2

2'1 x 2? Bottom-RT. 770 F 54. 5 82. 1 71. 8 46.9 69.9 24 63.8

the h istr set f r i E Example H same c em y as 0 th n xample I was heat The below tests were carried out using different steels of varying thicknesses as indicated.

treated according to the below schedule. The specimens program cooled showed good agreement in terms of properties with the 2T block specimens.

HEAT TREATMENT Normalize, 1675 F., 1 hr./in. Air cool Temper, 1,250 F., 1 hr./in. Air cool Stress relieve cycles, 1,250 F., 1 hr./in. Furnace cool to 600 F.

Stress relieve cycles, 1,250 F., 1 hr./in. Furnace cool to 600 F.

Stress relieve cycles, 1,050 F., 1 hr./in. Furnace cool to 600 F.

Stress relleve cycles, 1,050 F., 1 hr./in. Furnace cool to 600 F.

Stress relieve cycles, 1,050 F., 1 hr./in. Furnace cool to 600 F.

Stress relieve cycles, 1,250 F., 1 hr./in. Furnace cool to 600 F.

Test Elongation Test Heat Treatment Test temp., 2% Yield Tensile percent Method location F. strength strength in 2" 2T Block Top- 52, 800 90, 100 28 Botto 46, 400 500 29 Program-cooled Top. 53, 600 83,500 30 Botto 51, 100 84, 900 28 2T Block Top. 43, 000 000 22 Botto 39, 400 69, 000 24 Program-cooled Top 38, 700 68, 300 26 Botto 40, 500 69, 300 24 I'I-A, II-B and II-C were normalized at 1675 F. one hour per inch and air cooled. lI-D and II-E were heated to 1575 F. one hour per inch and water quenched. All

Example IV A 3T block sample (A) was heat treated (normalized) according to the schedule listed below. A program cooled specimen (B) was prepared from the same steel using specimens were tempered at 1250 F. one hour per inch cooling curves obtained from the centerline and quarterand furnace cooled. Thereafter the specimens were stressline areas of the 3T block. The results of the test were as relieved at 1225 F. one hour per inch and allowed to follows: furnace cool. The cooli ig rates were as follows: II- A, HEAT TREATMENT 9.1 F./m1n.; I I-B, 9.5 F./r n1n., II-C, 9.25 F./m1n., Fflhrs" AC and II-D and -E, 17. 8 F./m1n. 1,225: F., 7hrs.,AC O

The chemistries of these steels were as follows: 1,275 21 hrs-i F0 Tensile Yield Percent strength, strength, Elong. Percent P S Or Mo Cu p.s.i. p.s.i. in 2 RA.

.009 .017 2.27 .92 .13 0 AOent rline 30,700 55,700 30 30.2 .008 .017 2.75 .95 .08 Aqua erline- 82,000 54,200 28 75.5 .00 .017 2,75 .95 0s BCenterhne 80,600 56,200 27 77.7 .010 .022 .10 .46 .15 B Quarterhne 83,600 59,600 29 80.1

Equivalent Elongation Reduction Test tempering .2% Yield Tensile percent of area, method parameter strength strength in 2 percent II-A 21 37.1 43, 300 75,500 P-C 37. 1 51, 700 78,500 11-13 2'1 37. 1 42, 500 54, 200 P-O 37. 1 41, 65,000 II-C 2T 37. 5 50,200 77,900 19-0 37. 5 49, 300 77, 500 II-D 3T 35.3 53,600 75,800 P-C 35. 3 52, 600 72, 500 II-E 3'1 35.3 53,000 70, 300 P-O 35. 3 00, 000 75, 500

In summary, to simulate the heating and cooling cycles of a thick plate, it is necessary to use a source of heat that upon being turned off will not retain heat. A quartz lamp is one example of a heat source that can be used. Also, the heating element and the furnace must be capable of cooling 01f faster than the specimen being treated and -a water-cooled furnace is operative for this purpose. If cooling needs to be hastened, inert gas can be introduced through existing openings in furnace. The gas flow may be regulated as desired and the electronic control will still prevent exceeding desired cooling rate. The chief requirement is that extremely close control over the temperature of the specimen be exercised.

From the foregoing it will be apparent that the specimen being heat treated cannot be insulated and it is essential that the heating element, preferably a quartz lamp, be of the modulating type so that all degrees between the highest and lowest temperatures can be quickly attained.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. A method of ascertaining the physical characteristics such as yield strength, tensile strength, percentage of elongation and percentage of reduction in area, of a steel plate which will exist after a predetermined heat treatment, which comprises (1) recording the heating and cooling rates which occur during heat treatment substantially identical to the desired predetermined heat treatment taken at a standard test location within a steel plate of similar chemistry and thickness,

(2) preparing, a comparatively small test piece from a depth corresponding to the depth of said standard test location from the plate to be tested,

(3) afiixing a control thermocouple to said test piece,

(4) heating said assembled test piece to predetermined temperatures for predetermined lengths of time corresponding to said recorded heating rates in a furnace,

(5) controlling by said thermocouple the reduction of temperature of said furnace at a rate whereby said test piece is cooled at said recorded cooling rate whereby the cooling rate of said test piece is substantially the same as the cooling rate of steel at about said standard test location in said plate to be tested, and

(6) testing sai-d test piece to determine its physical characteristics.

2. A method in accordance with claim 1 wherein said test piece is also heated at a rate corresponding to said recorded heating rate.

References Cited UNITED STATES PATENTS 2,262,778 11/1941 Schneider 73--15 2,729,096 1/1956 Rosenholtz et a1. 73--15.6 3,129,087 4/1964 Ha-gy 7315.6

JAMES J. GILL, Primary Examiner.

ROBERT S. SALZMAN, Assistant Examiner. 

